SUMMARY OF PROPOSAL 51057

SPECTROSCOPY OF AN X-RAY PULSAR OAO 1657-415 THROUGHOUT THE ECLIPSE TRANSITION

ABSTRACT

From recent Timing observation, the CGRO BASTE determined that the 38-s X-ray pulsar OAO 1657-415 is an eclipsing binary with an orbital period 10.4436, and eclipse duration 1.70 d. Hence, this binary pulsar, OAO 1657-415 is a system very similar with Vela X-1; they are just twin. We propose to observe this X-ray pulsar throughout its eclipse transition covering the phase of full eclipse, pre-eclipse ingress and post-eclipse egress. From the observation we investigate (1) iron emission during non-eclipse phase if it is 6.6 keV as was reported, (2) recombination emission lines from photo-ionization plasma during eclipse, (3) companion star atmosphere from eclipse transion, and (4) interstellar dust halo from soft-band image. These results will be compared with those of Vela X-1.